Polyolefins such as high density polyethylene (HDPE) homopolymer and linear low density polyethylene (LLDPE) copolymer can be produced using various combinations of catalyst systems and polymerization processes. Metallocene-based catalysts systems, for example, typically contain a metallocene compound and an activator. It is well established that the structure of the metallocene compound can impact the polymerization process and the resulting polymer properties, including molecular weight parameters such as weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (MWD). In contrast, the present invention is directed generally to the impact of the activator on the polymerization process and the resulting polymer properties, for example, the Mw and Mn of the polymer.